1,I-Dichloro-1-fluoroethane is presently under consideration as a replacement for trichlorofluoromethane as a foam blowing agent. It has a substantially lower ozone depletion index than trichlorofluoromethane. Moreover, 1,I-dichloro-1-fluoroethane displays a 10-15% greater blowing efficiency in rigid foam, and improved solubility in aromatic polyester polyol, in comparison to trichlorofluoromethane.
In the manufacture of 1,1-dichloro-1-fluoroethane and 1-chloro-1,1-difluoroethane, by-products are generated. 1,1,1-Trichloroethane is susceptible to dehydrohalogenation, which leads to the formation of vinylidene chloride. The latter is a particularly undesirable by-product, since it is a suspected carcinogen. Vinylidene chloride and 1,1-dichloro-1-fluoroethane boil at 31.degree. C. and 32.degree. C., respectively. Thus, they cannot be readily separated by distillation.
2,2,4,4,4-Pentafluorobutane is another undesirable by-product of the fluorination of 1,1,1-trichloroethane. I believe that it is formed by the reaction between 1,1,1-trichloroethane and vinylidene chloride, followed by the reaction of additional 1,1,1-trichloroethane with vinylidene chloride to give 1,1,1,3,3-pentachlorobutane. Grigor'ev et al., Izv. Akad. Nauk. SSSR. Ser. Khim., 6, 1333-6 (1980). Hydrofluorination of the latter produces 2,2,4,4,4-pentafluorobutane.
2,2,4,4,4-Pentafluorobutane is the principle organic component of reactor bottoms or "tars"which are typically generated in the fluorination of 1,1,1-trichloroethane, particularly at high temperatures. The build-up of tar substances as reactor bottoms effectively slows the production rate to a point where the reaction mixture must be dumped.
Several approaches have been developed to eliminate the co-production of tars and/or vinylidene chloride in the fluorination of 1,1,1-trichloroethane.
U.S. Pat. No.2,894,044 discloses the vapor phase fluorination of 1,1,1-trichloroethane to 1,1-dichloro-1-fluoroethane by hydrogen fluoride over a catalyst selected from the group of stannic fluoride on activated carbon and aluminum fluoride. The patentee states that under certain conditions these catalysts cause fluorination of I,1,1-trichloroethane without appreciable dehydrohalogenation. Despite this statement, the examples of U.S. Pat. No. 2,894,044, evidence substantial co-production of vinylidene chloride.
U.S. Pat. No. 3,833,676 discloses a non-catalytic process for the fluorination of 1,1,1-trichloroethane to give 1,1-dichloro-1-fluoroethane and 1-chloro-1,1-difluoroethane. However, the process requires a molar ratio of hydrogen fluoride to 1,1,1-trichloroethane of at least 4:1. The process has little selectivity for 1,1-dichloro-1-fluoroethane.
Henne et al., J. Am. Chem. Soc., 70, 758-60 (1945) reported that the addition of hydrogen fluoride to olefins in the liquid phase may be accelerated in the presence of boron trifluoride. The reaction was characterized by low conversion, and polymer formation. Despite this teaching, it has not been heretofore known that the fluorination of 1,1,1-trichloroethane to selectively produce 1,1-dichloro-1-fluoroethane substantially free of vinylidene chloride and polymer formation, may be carried out.